1. Field of the Invention
The present invention relates to a driving system for use in camera and especially to a diaphragm driving system and/or a mirror driving system. More particularly, the present invention relates to a mechanical apparatus for driving diaphragm and/or mirror in a camera.
2. Description of Prior Art
In the art there are known various types of automatic aperture control apparatus for camera. In one of the typical automatic aperture control apparatus, when the diaphragm aperture continuously changing toward the minimum aperture from the maximum reaches the position corresponding to the aperture value determined by the result of a photometric operation, it is detected. In synchronism with the detection, the mechanism moving to drive the diaphragm blade is latched by electromagnetic means or the like. Since the diaphragm blade driving mechanism is so designed as to be shifted from one position to another to drive the diaphragm blade, it is essential to suitably reduce the moving speed of the shifting mechanism in order to improve the accuracy of diaphragm control. The reason for this will be described in detail hereinafter.
In the above mentioned type of control apparatus, the electromagnetic latching device has inevitably a time lag in operation. Therefore, at least a short time before the electromagnetic device is actuated, the moving speed of the shifting mechanism should be reduced to a level sufficient and enough to set the desired diaphragm aperture value. Otherwise, there may be produced a large error in setting the aperture value.
The time lag may be compensated by an early actuation of the electromagnetic latching device. More particularly, some time before the diaphragm aperture reaches the predetermined aperture value an instruction signal is applied to the electromagnetic device to start the latching operation. However, this solution involves many problems.
In the case of lens interchangeable camera of the type in which many different interchangeable lenses are adoptable and the diaphragm driving lever on the lens side is moved together with the above mentioned displacement mechanism in the camera, it is very difficult to correctly compensate the time lag employing the above solution. The reason for this is that the respective interchangeable lenses are different each other in inertia of the lens diaphragm.
Even for those cameras having one and single lens, the use of the above solution makes structure of the camera much more complicated and also increases up the manufacturing cost.
Another drawback of the above solution is that it is impossible to accurately determine the aperture value. This problem of inaccurate aperture value may be solved by reducing the driving force used for shifting the displacement mechanism. However, since the displacement mechanism has an inherent frictional loss, the stability of its operational speed may be greatly lost by such reduction of the driving force. To overcome the difficulty, therefore, such reduction system is required which can reduce the speed in a stable manner while using a sufficiently large driving force. Such reduction system can be realized only when there are provided particular inertia brake, mechanical clock mechanism and electromagnetic brake. Even if such reduction system can be obtained, it has to be returned back to the starting position every time of operation. This needs a large returning force. Furthermore, the use of such reduction means will make the structure of the apparatus very complicated. At the same time, the work required to operate such reduction mechanism will directly or indirectly cause a substantial increase of the power of the camera required to take up film.